This invention relates to a diaphragm pump with a hydraulically powered diaphragm.
Growing environmental protection requirements, combined with strict legal requirements, can be met mostly only with the help of hermetically sealed process systems. Non-leaking fluid machines such as, for example, pumps and condensers, are of the utmost importance in this connection. Diaphragm pumps constitute an optimum solution, especially for delivering toxic, hazardous, annoying, sensitive, abrasive, corrosive fluids as well as for aseptic conditions. The diaphragm, as the central element, performs the double function of static seal and displacers in the form of an elastic delivery chamber wall. The static diaphragm seal is the basis for the hermetic tightness of diaphragm pumps. The diaphragm furthermore transmits the oscillating stroke motion of a drive through the fluid that is to be delivered, as a result of which, it is not only the pulsating delivery that materializes, but there is also an interaction with the fluid masses in the pipeline system. In the case of diaphragm pumps with hydraulic diaphragm drive, the oscillating motion of a drive member is transmitted via a hydraulic sealxe2x80x94which comprises a hydraulic fluidxe2x80x94to the diaphragm. The hydraulically driven diaphragm always works with balanced pressure and need withstand only deflection stresses.
PTFE (polytetrafluoroethylene) proved effective in diaphragm pump engineering due to its outstanding chemical stability and the good physical properties so that it became the standard material for diaphragms. Customary diaphragm designs are pure PTFE diaphragms with rotationally symmetrical shaft contour or flat contour and PTFE as protective layer on elastomer diaphragms.
The limit for the use of PTFE as diaphragm for diaphragm pumps currently is found at a delivery pressure of 350 bar and a temperature of 150xc2x0 C. The reasons for these limitations are found in the cold-flow resistance that is no longer adequate and the tight sealing pressure of the PTFE in the diaphragm chucking. By means of design measures, for example, by means of a suitable ribbed structure, it has been possible to counteract the cold flow within limits. The ribbing prevents the diaphragm material from flowing out of the diaphragm chucking. As a result, one can raise the flow limit in the diaphragm chucking to values that are far above the yield stress from the tensile test.
Above 350 bar, there is also the fact that the parts between which the diaphragms are chucked, that is to say, the pump as such and the chuck drive housing are deformed by the change of pressure in the pump, which results in a certain xe2x80x9crespirationxe2x80x9d in the chucking. This term xe2x80x9crespirationxe2x80x9d refers to a decrease of the press-on pressure between the pump lid and the pump housing in the chucking area of the diaphragm, a decrease that keeps recurring possibly periodically during the operation of the diaphragm pump. The respiration increases with increasing pressure and growing structural size. The potential for elasticity adjustment by way of the diaphragm, however, is very limited so that this likewise creates a limit for any increases in the pressure and the structural size. Furthermore, the constantly recurring stress change of the diaphragm due to respiration constitutes a severe mechanical stress or dynamic alternating stress and after a corresponding span of time leads to the fatigue of the diaphragm material and finally to a destruction of the diaphragm. This action mechanism has so far not been recognized in this form.
The object of the invention therefore is to provide a diaphragm pump of the kind mentioned above, which eliminates the above-mentioned disadvantages and which can be used also at higher delivery pressures and higher operating temperatures with a long diaphragm service life. At the same time, the idea is to counteract the negative effect of xe2x80x9crespirationxe2x80x9d of the pump head in the area of the diaphragm chucking.
In the invention-based diaphragm pump, there is provided in the chucking area additionally at least one elastic part that is so designed that it will elastically adjust any reductions occurring during the operation of the diaphragm pump in the press-on pressure in the chucking area of the diaphragm between the pump lid and the pump housing.
This design offers the following advantage: the diaphragm pump is suitable also for high pressure, for example, above 350 bar, and for higher temperatures, for example, over 150xc2x0 C. because deformations of pump lid and pump housing occurring in this area and possibly leading to a decline in the press-on pressure in the chucking area are effectively compensated. At the same time, a cold flow strength and tight sealing pressure of the diaphragm material that under certain operating conditions might possibly no longer be sufficient is also compensated. In other words, the invention-based arrangement increases the elasticity of the diaphragm in the chucking area so that the minimum pressure required for a tight seal is preserved in the chucking area of the diaphragm also in case of deformation of the parts that are involved in the chucking area. The elastic part that is provided according to the invention does not have any sealing function here; instead, it serves for the compensation of fluctuations in the press-on pressure in the chucking area of the diaphragm.
The elasticity reserves of a diaphragm packet are increased by virtue of the fact that the diaphragm comprises two or more material layers with at least one elastic part being arranged between at least two layers. Here, the elastic part, for example, is made as an elastic intermediate layer or as elastic intermediate ring.
The elastic part is advantageously made as a weft in order to ensure a fluid-conducting connection between the internal chamber between the two material layers of the diaphragm and a diaphragm rupture sensor.
The elastic part extends over the entire circumference of the diaphragm so as to compensate for any material deformations over the entire chucking area within the direction of circumference.
The elastic part can be arranged on one side or on both sides of the diaphragm.
In a preferred embodiment, the elastic part comprises one or several elastomer O-rings. As an alternative, the elastic part is made as a lip seal.
The elastic part is an integral part of the diaphragm for simple and quick assembly.
In a practical manner, the diaphragm is made of PTFE or PE or, as an alternative, it is made of an elastomer with a protective layer consisting of PTFE.